Arc gap circuits for flashing high voltage photoflash lamps

ABSTRACT

Circuit arrangements of arc gaps in series with high-voltage photoflash lamps, for improving reliability of flashing and for causing sequential flashing of individual lamps of an array of photoflash lamps by means of high-voltage firing pulses such as are produced by impacting a piezoelectric element in synchronism with the opening of a camera shutter.

United States Patent [191 Cote [111 3,742,298 June 26, 1973 ARC GAPCIRCUITS FOR FLASHING HIGH-VOLTAGE PI-IOTOFLASII LAMPS [75] Inventor:Pau1T.C0te,Cleveland Heights.

Ohio

[73] Assignee: General Electric Company, Schenectady,N.Y.

[22] Filed: Mar. 24, 1971 [21-] Appl. No.: 127,562

[52] US. Cl....-. 315/323, 315/69, 431/95,

. 4'31/DIG. 3

[51] Int. CI.. H051) 37/00, I-IOSb 41/34, G03b 15/04 [58] Field ofSearch 315/323, 289, 171, 315/69; 431/9298; 95/11.5 R, 11.5 A

[5 6] References Cited UNITED STATES PATENTS 1/1965 Kopito 431/92 X10/1970 Cote et al.

' 3/1970 Yando 95/l1.5 R X 3,528,354 9/1970 Nakagawa. 431/95 X FOREIGNPATENTS OR APPLICATIONS 404,577 H1969 Australia 95/1 1' L PrimaryExaminer-Rudolph V. Rolinec Assistant ExaminerMarvin NussbaumAttorney-Norman C. Fulmer, Henry P. Truesdell, Frank L. Neuhauser, OscarB. Waddell and Joseph B. Forman [57] ABSTRACT Circuit arrangements ofarc gaps in series with highvoltage photoflash lamps, for improvingreliability of flashing and for causing sequential flashing ofindividual lamps of an array of photoflash lamps by means ofhigh-voltage firing pulses such as are produced by impacting apiezoelectric element in synchronism with the opening of a camerashutter.

7 Claims, 4 Drawing Figures PAIENIEUmas ms Inventor:

Paul, T. co=t 33 g y j as His A=ttorne Fig. 4.

ARC GAP CIRCUITS FOR FLASHING HIGH-VOLTAGE PHOTOFLASH LAMPS BACKGROUNDOF THE INVENTION flashing of the individual lamps of an array of flashlamps.

Photoflash lamps may be classified generally into two voltage types:low-voltage and high-voltage. The lowvoltage types usually are intendedto beflashed by a battery, or a charged capacitor, having a voltage ofabout 1.5 volts to volts, whereas the high-voltage flash lamps areintended to be flashed by a firing pulse of a few hundred volts orgreater such as can be produced by a piezoelectric element.

Low-voltage flash lamps have achieved commercial success, and variousmechanisms have been developed for flashing individual lamps, and alsofor flashing, oneat-a-time, lamps of a multiple-lamp arrangement such asthe popular flashcube. Also, various designs have been proposed for anarray of flash lamps having reflectors associated therewith fordirecting the light from all of the lamps in the same direction. Variousswitching mechanisms and circuits have been devised for causing thelamps of the array to flash, one-at-a-time, each time a camera shutteris opened to take a picture. An advantage of such an array is that itneed not be moved or rotated between flashes as is the case with theflashcube.

High-voltage flash lamps, in contrast to the lowvoltage type, have notachieved appreciable commercial success, in spite of their importantadvantageous capability of being flashed by means of a small,lightweight, and longlife piezoelectric element and hence not requiringthe use of heavy and bulky batteries with" their attendant drawbackssuch as requiring recharging or replacement and which frequently fail toprovide adequate firing pulse energy due to their connections beingloose, dirty, oxidized or corroded. An obstacle in the path ofcommercial success of the high-voltage type of flash lamp, is that manyswitching mechanisms and firing circuits usable for low-voltage lampsare unsuited or unfeasible for use with high-voltage lamps. Also, therate-of-rise time of firing pulses produced by a piezoelectric elementtends to be somewhat too slow for insuring optimum flashability oftypical flash lamps.

SUMMARY OF THE INVENTION Objects of the invention are to provideimproved circuitry for reliably flashing high-voltage flash lamps, andto provide circuits for causing sequential individual flashing of thelamps of an array of high-voltage flash lamps from sequentialhigh-voltage firing pulses produced insynchronism with a camera shuttereach time a flash picture is to be taken.

The invention comprises, briefly and in a preferred embodiment, an arcgap connected in electrical series combination with a high-voltage flashlamp, this series combination being adapted for connection across asource of high-voltage firing pulses. An embodiment of the inventioncomprises a plurality of high-voltage flash lamps, and a plurality ofarc gapsof differing voltage breakdown characteristics respectivelyconnected in series combinations with the flash lamps, these seriescombinations being connected in a parallel combination adapted forconnection across a source of highvoltage firing pulses. A furtherembodiment comprises a plurality of high-voltage flash lamps, and aplurality of arc gaps successively connected in series between the flashlamps so as to connect the lamps in electrical parallel combinationthrough the arc gaps, an end of this parallel combination being adaptedfor connection across a source of high-voltage firing pulses.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagram, partly pictorialand partly schematic, of a preferred embodiment of the invention;

FIG. 2 is a diagram of an alternative preferred embodiment of theinvention;

FIG. 3 is a diagram of a further alternative preferred embodiment of theinvention; and

FIG. 4 illustrates an arc gap modification that may be incorporated inFIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a source 11 of firingpulse energy comprises a piezoelectric element 12 which may be in theform of a small cylinder having electrodes 13 and 14 at the top andbottom thereof, connected respectively to firing pulse terminals 16 and17. An impactor 18 is car ried at the end of an elongated spring 19, theother end of which is fixed by means 20 which may be carried by a camerahousing or in a shutter mechanism. The irri-v pactor 18 may be arrangedto be raised away from the piezoelectric element 12 when the camerashutter is cooked, and released upon opening of the shutter to take apicture whereupon the spring 19 urges the impactor 18 in the directionof the arrow 21 so as to impact against the piezo-electric element 12thereby producing a firing pulse at the terminals 16 and 17. Thepiezoelectric element 12 may be, for example, approximately one-eighthinch in diameter and one-fourth inch long, and may be made from bariumtitanate, lead metaniobate, PZT (lead-zirconium-titanate) or othersuitable piezoelectric material. Further details of piezo electric meansfor producing photoflash firing pulses, andcamera synchronizing means,are disclosed in U.S. Pat. Nos. 2,972,937 and 3,106,080, both toChauncey G. Suits and assigned to the same assignee as the presentinvention.

A high-voltage photoflash lamp 26, having the usual glass envelopecontaining shredded metal foil 27, is provided with a pair of electrodes28 and 29 extending within the lamp. One or both of the electrodes 28and 29 is coated-with a primer material. The metal foil 27 is in contactwith both of the electrodes 28 and 29 and- /or their primer coatings, sothat when a high-voltage firing pulse is applied to these electrodes,the circuit is completed through the shredded metal foil 27 wherebynumerous sparks occur in theprimer material, thereby igniting the primerand causing the bulb to flash. Lead wires 31 and 32 are respectivelyconnected to the electrodes 28 and 29. Further details of a high-voltagephotoflash lamp are disclosed in U.S. Pat. No. 2,868,003 to Warren F.Albrecht and assigned to the same assignee as the present invention.Such a lamp may be flashed by means of a firing pulse of approximately500 volts. Filament type flash lamps may be employed, if the filament isof sufficiently high resistance for causing the lamp to be flashed by ahigh-voltage, low-current firing pulse. 1

An arc gap 33 is connected between one of the firing pulse terminals 16and one of the lead wires 31 of the lamp 26, the other firing pulseterminal 17 being connected to the other lead wire 32 of the lamp 26,thus connecting the electrodes of lamp 26 across the firing pulseterminals 16 and 17, in series with the arc gap 33. The are gap 33comprises a pair of spaced-apart electrodes 34 and 35, which may bewires or other electrical conductors suitably positioned to define anair gap of, for example, about one-thousandth of an inch. Alternatively,the arc gap 33 may comprise a dielectric gap, composed of a pair ofconductors such as wires spaced apart by a thin piece of dielectricmaterial such as a polymer, designed so that the arc gap will break downat a few hundred volts.

The circuit of FIG. 1 functions as follows. When the piezoelectricelement 12 is impacted by the impactor 18, in synchronism with theopening of a camera shutter, the piezoelectric element 12 becomesstressed and produces a voltage pulse of approximately 1000 to 2000volts, for example, depending somewhat upon the force of impact. Whenthe rising wavefront of the firing pulse voltage, which is impressedacross the arc gap 33 through the high-resistance conductive path of thelamp 26 (since no current is flowing at this time, there will be novoltage drop through the lamp 26) reaches 1 the breakdown potential ofthe arc gap 33, the gap 33 will break down and provide a relatively lowresistance path for the high-voltage firing pulse to reach the lamp 26,causing it to flash. Since the arc gap 33 breaks down only when thewavefront of the high-voltage pulse has reached a few hundred volts orso, it insures that the lamp 26 will receive a sudden burst of firingpulse energy, thereby insuring that even stubbom" lamps will flash.

If desired, a plurality of additional flash lamps 26' may be connectedin parallel with the first lamp 26, these lamps having relativelydifferent firing voltage characteristics so that each occurrence of afiring voltage pulse will cause flashing of only that one unflashed lampin the circuit having the lowest flashing voltage characteristic. Thus,each time a flash picture is to be taken, the high-voltage firing pulsecauses flashing of one of the plurality of lamps of the array, the lampsall being arranged with reflectors so as to direct theirlight in thesame given direction. For this purpose the arc gap 33 should be an airgap, which has repeatable breakdown characteristics, rather than adielectric gap which does not have repeatable breakdown characteristics.The array of flash lamps may be provided with connectors 36 and 37adapted to plug into or otherwise removably engage the high-voltagefiring pulse terminals 16 and 17 which may be provided on a camera or ona flash adaptor attachment.

In FIG. 2, an electrical conductor 38 is connected to the connector 36which is adapted to engage firing pulse terminal 16, and an electricalconductor 39 is connected to the connector 37 which is adapted to engagefiring pulse terminal 17. A plurality of highvoltage flash lamps 41, 42,43, 44 is provided, each of which may be similar to the lamp 26described above, and each provided with a reflector adapted to directthe light from the lamps in the same given direction from the array oflamps. One lead wire 41a, etc., of each of the flash lamps 41-44 isconnected to the electrical conductor 38, and the other lead wires 41b,etc., are respectively connected to the conductor 39 via individual arcgaps 46, 47, 48 and 49. Thus, each flash lamp is in series combinationwith its associated arc gap, and these series combinations are connectedin parallel witheach other across the conductors 38 and 39. The arc gaps46-49 are designed to break down at different voltages. This may beachieved, with air gaps, if one of the arc gaps 46 has a spacing of 0.5thousandths of an inch, another one 47 has a gap spacing of 1.5thousandths of an inch, another 48 a gap spacing of 3 thousandths of aninch, and the remaining gap has a gap, spacing of 5 thousandths of aninch. The are gaps may also be specified in terms of their breakdownvoltage, for example the gap 46 may be designed to break down at 300volts, gap 47 at 600 volts, gap 48 at 900 volts, and gap 49 at 1200volts.

The circuit of FIG. 2 functions as follows. Upon the first occurrence ofa firing pulse at terminals 16 and 17, the lowest voltage breakdown gap46 breaks down and the lamp 41 becomes flashed; there is insufficientfiring pulse energy to break down anyof the other arc gaps, and henceonly the one lamp 41 will be flashed by the firing pulse. Upon flashing,the lamp becomes an open circuit, so that when the next firing pulseoccurs, the lowest breakdown voltage gap associated with an unflashedlamp, i.e., the gap 47, will break down and the second lamp 42 willbecome flashed. This procedure repeats until all of thelamps have beenflashed. It may first appear that the voltage breakdown of a gap becomessubtracted from the firing voltage applied to the associated lamp, andhence the last lamp 44, associated with the widest-spaced arc gap 49,might not reliably flash. However, this is not the case. Assume, forexample, that the lamp 44 will flash at 500 volts of firing pulsevoltage, the arc gap 49 breaks down at 1200 volts, and the firing pulseapplied to the terminals 16 and 17 has a peak voltage of 1500 volts. Thearc gap 49 will break down at 1200 volts, and the arc will have avoltage drop of only a few volts, the actual voltage drop dependingsomewhat on the arc current so that a peak voltage of about 1500 voltswill be applied to the lamp 44, which is adequate for insuring reliableflash- If desired, an additional flash lamp 51 may be connected acrossthe conductors 38 and 39, and will be the first to be flashed sincethere is no arc gap in series with it. Also, if desired, an additionalarc gap 33, shown in FIG. 4, can be inserted between the points x and yin the conductor 39 of FIG. 2, between the connector 37 and the flashlamps, and will function upon each lamp flashing as described above inconnection with FIG. 1.

The circuit of FIG. 3 comprises a plurality of highvoltage flash lamps56-60 with the a lead wires thereof all connected to the conductor 38which is connected to a connector 36 adapted to be removably connectedto the firing pulse terminal 16, as in FIG. 2 above. The b lead wire ofthe first lamp 56 is connected to the connector 37 which is adapted tobe connected to the firing pulse terminal 17 A plurality of arc gaps61-64 are successively connected between the b lead wires of the lamps56-60.

The circuit of FIG. 3 functions as follows. Upon occurrence of the firstfiring pulse, the first lamp 56 will =flash, since it receives the fullfiring pulse energy because the arc gap 61 does not breakdown and henceit prevents the firing pulse energy from reachingany of the other flashlamps. Upon the occurrence of a second firing pulse, the first lamp 56is an open circuit, and hence the arc gap 61 will break down (becausethe firing pulse voltage is applied across it via the lamp 57) and thesecond lamp 57 will flash. A third firing pulse causes the first andsecond arc gaps 61 and 62 to break down, and the third lamp 58 willbecome flashed. This procedure continues, with additional numbers of arcgaps breaking down, until all of the flash lamps have been flashed. Itmay first appear that in order for the four are gaps 61-64 to break downso that the last lamp 60 can flash, the required total breakdown voltagemust be the sum of the individual breakdown voltages of the four arcgaps, and hence there may be doubt as to the reliability of the lastlamp 60 becoming flashed. However, the plurality of series arc gaps willbreak down at less than the total sum of the individual breakdownvoltages. This is due to differing capacitances across the arc gaps,which may be at random or may be designed into the construction of thearc gaps. The firing pulse voltage distribution across the variousseriesconnected arc gaps will be distributed so that the greatest amountof voltage across an arc gap will be across that are gap having theleast capacitance between its electrodes, and when this arc gap breaksdown and arcs, the rest of the arc gaps will quickly and readily breakdown and arc. For example, if all but the last lamp 60 have beenflashed, and a firing pulse of 1500 volts is applied to the terminals 16and 17, and each of the arc gaps 61-64 individually will break down atabout 500 volts, and the lamp 60 requires 500 volts to flash, thevoltage distribution of the 1500 volts across the series-connected arcgaps will be such that more than 500 volts will appear across one of thegaps, causing it to break down, whereupon the other are gaps quicklybreak down, and, assuming a few volts drop at each arcing gap, the totalare gap voltage drop will be less than 100 volts, whereupon more than1400 volts of the firing pulse will exist across the electrodes of Ilamp 60 thereby causing it to flash. The are gaps 61-64 may bedesignedfor similar, or differing, breakdown voltage characteristics forachieving optimum results. If desired, an additional arc gap 33, asshown in FIG. 4, may be inserted between the points x and y in FIG. 3,in a manner similar to that described above for FIG. 2. Preferably, thearc gap 33 is interposed in the conductor 39, as shown, which results ina lower capacitance across the gap than if the gap were interposed inthe conductor 38 where it would have a higher capacitance thereacrossdue to stray capacitance of the lamp wiring. The lower gap capacitanceimproves the repetitive uniformity of breakdown voltage. The terminal 16and conductor 38 should be considered as being the electrical ground ofthe circuit and may be connected electrically to the camera case orshutter mechanism. It will be apparent that the invention, as describedabove, achieves'a simple, light-weight, compact, and economical circuitfor reliably flashing one or a plurality of high-voltage flash lamps.The are gaps may be manufactured extremely economically, as each arc gapmay comprise spaced-apart wires. In an even more economicalconstruction, one of the electrodes of each arc gap may be the lead wireof the associated flashlamp, this lead wire being suitably spaced fromanother circuitwire, or from a printed-circuit conductor.

While preferred embo'dimeiitsof theiriventionand modifications thereofhave'be'en' shown and described, various other embodiments'a'nd'modifications will become apparent 'to'pe'rsons skilled in the art, andwill fall within the scope of invention as defined in the followingclaims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A photoflash circuit comprising a high-voltage photoflash lampadapted to be flashed by a firing voltage, and an arc gap connected inelectrical series with said flash lamp, said are gap comprising a pairof spaced-apart electrodes having air therebetween and adapted to breakdown and are in the air between said electrodes in response to saidfiring voltage being applied across the series combination of said flashlamp and arc gap, said circuit including at least one additionalhigh-voltage flash lamp connected in electrical parallel with saidfirst-named flash lamp, said flash lamps having relatively differentflashing voltage characteristics.

2. A photoflash circuit comprising a high-voltage photoflash lampadapted to be flashed by a firing voltage, and an arc gap connected inelectrical series with said flash lamp, said are gap comprising a pairof spaced-apart electrodes having air therebetween and adapted to breakdown and arc in the air between said electrodes in response to saidfiring voltage being applied across the series combination of said flashlamp and are gap, said circuit including a piezoelectric firing pulsegenerator, and means connecting the series combination of said flashlamp and said arc gap across the output of said piezoelectric firingpulse generator.

3. A photoflash circuit for causing sequential flashing of a pluralityof high-voltage photoflash lamps by means of sequential firing voltagepulses, comprising a plurality of arc gaps respectively connected inelectrical series with said plurality of flash lamps thereby forming aplurality of series combinations, and means connecting said seriescombinations in an electrical parallel combination adapted to beconnected across a source of said firing pulses, said are gaps havingrelatively different voltage breakdown values with respect to oneanother, said voltage breakdown values being less than the voltage ofsaid firing voltage pulses.

4. A circuit as claimed in claim 3, including an additional arc gapconnected in electrical series with said parallel combination so as tobe interposed between said parallel combination and said source offiring pulses.

5. A circuit as claimed in claim 3, including an additional high-voltageflash lamp connected directly in electrical parallel with said parallelcombination.

6. A circuit as claimed in claim 5, including an additional arc gapconnected in electrical series with the parallel circuit of saidparallel combination and said additional lamp so as to be interposedbetween said parallel circuit and said source of firingpulses.

7. A photoflash circuit for causing sequential flashing of a pluralityof high-voltage photoflash lamps by means of sequential firing voltagepulses, comprising means including a plurality of arc gaps successivelyconnected in electrical series between said plurality of flash lamps soas to connect the lampsin an electrical parallel combination throughsaid arc gaps, and means adapted for connecting an end of said parallelcombination across a source of said firing pulses, said are gaps eachcomprising a pair of spaced-apart electrodes nected in series with saidparallel combination so as to having air therebetween and having avoltage breakbe interposed between said parallel combination and downvalue less than the voltage of said firing voltage said source of firingpulses. pulses, said circuit including an additional arc gap con-

1. A photoflash circuit comprising a high-voltage photoflash lampadapted to be flashed by a firing voltage, and an arc gap connected inelectrical series with said flash lamp, said arc gap comprising a pairof spaced-apart electrodes having air therebetween and adapted to breakdown and arc in the air between said electrodes in response to saidfiring voltage being applied across the series combination of said flashlamp and arc gap, said circuit including at least one additionalhigh-voltage flash lamp connected in electrical parallel with saidfirst-named flash lamp, said flash lamps having relatively differentflashing voltage characteristics.
 2. A photoflash circuit comprising ahigh-voltage photoflash lamp adapted to be flashed by a firing voltage,and an arc gap connected in electrical series with said flash lamp, saidarc gap comprising a pair of spaced-apart electrodes having airtherebetween and adapted to break down and arc in the air between saidelectrodes in response to said firing voltage being applied across theseries combination of said flash lamp and arc gap, said circuitincluding a piezoelectric firing pulse generator, and means connectingthe series combination of said flash lamp and said arc gap across theoutput of said piezoelectric firing pulse generator.
 3. A photoflashcircuit for causing sequential flashing of a plurality of high-voltagephotoflash lamps by means of sequential firing voltage pulses,comprising a plurality of arc gaps respectively connected in electricalseries with said plurality of flash lamps thereby forming a plurality ofseries combinations, and means connecting said series combinations in anelectrical parallel combination adapted to be connected across a sourceof said firing pulses, said arc gaps having relatively different voltagebreakdown values with respect to one another, said voltage breakdownvalues being less than the voltage of said firing voltage pulses.
 4. Acircuit as claimed in claim 3, including an additional arc gap connectedin electrical series with said parallel combination so as to beinterposed between said parallel combination and said source of firingpulses.
 5. A circuit as claimed in claim 3, including an additionalhigh-voltage flash lamp connected directly in electrical parallel withsaid parallel combination.
 6. A circuit as claimed in claim 5, includingan additional arc gap connected in electrical series with the parallelcircuit of said parallel combination and said additional lamp so as tobe interposed between said parallel circuit and said source of firingpulses.
 7. A photoflash circuit for causing sequential flashing of aplurality of high-voltage photoflash lamps by means of sequential firingvoltage pulses, comprising means including a plurality of arc gapssuccessively connected in electrical series between said plurality offlash lamps so as to connect the lamps in an electrical parallelcombination through said arc gaps, and means adapted for connecting anend of said parallel combination across a source of said firing pulses,said arc gaps each comprising a pair of spaced-apart electrodes havingair therebetween and having a voltage breakdown value less than thevoltage of said firing voltage pulses, said circuit including anadditional arc gap connected in series with said parallel combination soas to be interposed between said parallel combination and said source offiring pulses.